The present invention relates to an ultrasonic nebulizer, and more particularly to a device for indicating an abnormal condition in the nebulizer such as by generating an alarm signal when the level of liquid in the nebulizer falls below a predetermined level.
It is known to sense liquid level in an ultrasonic nebulizer and to terminate oscillation and consequent nebulizing of the liquid when liquid level falls below a predetermined value (see U.S. Pat. No. 3,989,042). However, there is no means for informing an operator that the liquid is not present in the nebulizing container. Therefore, the operator cannot judge whether the system has been stopped due to an absence of liquid in the container or the system has been shut down due to some other problem. Additionally, there is no signal indicating a need for liquid to be supplied to the system, so that liquid may not be supplied for a long period of time, and the humidity generating function, e.g., of the system will be destroyed. In order to generate an alarm signal showing an absence of liquid, it may be possible to provide an additional float switch and thereby to operate such alarm device as a lamp or buzzer. However, such a prior art system requires an additional float switch, which complicates the entire system and increases the manufacturing cost.
It is thus an object of the present invention to provide an ultrasonic nebulizer in which only one float switch is used, and an alarm signal is generated and the oscillating operation in the circuit is terminated when an absence of liquid is determined.
The present invention finds application in an ultrasonic nebulizer that includes a container for storing a liquid therein, a transducer located substantially at the bottom part of the container to apply an ultrasonic wave to the liquid and to nebulize the same, an oscillator for energizing the transducer, a float switch for sensing the presence of liquid in the container, means for controlling a biasing voltage in the oscillator dependent upon the output at the float switch and terminating oscillation when liquid falls below a certain level in the container, and an alarm means connected to the float switch. The invention involves use of a two-terminal float switch so that when the liquid level in the container falls below that predetermined level, the float switch is released and a biasing current is no longer applied to the oscillator circuit; at the same time an alarm signal is generated.
The invention will be more completely understood by reference to the following detailed description.